Enhancing the production of aromatics in high temperature, high space velocity catalytic conversion of lower molecular weight hydrocarbons to higher molecular weight hydrocarbons

ABSTRACT

In a continuous catalytic process for the production of higher molecular weight hydrocarbons from lower molecular weight hydrocarbons in which a lower molecular weight hydrocarbon containing gas is contacted in a reaction zone with a higher molecular weight hydrocarbon synthesis catalyst under C 2  + hydrocarbon synthesis conditions, the improvement comprising adding hydrogen to said gas thereby forming a reaction gas wherein said hydrogen comprises 1 to 25 volume percent of the reaction gas, said synthesis conditions including a temperature greater than 1000° C. and a gas hourly space velocity of greater than 3200 hr -1 .

FIELD OF THE INVENTION

The present invention relates to a catalytic process for the productionof higher molecular weight hydrocarbons from lower molecular weighthydrocarbons. More particularly, the present invention is concerned withthe production of aromatic hydrocarbons in a catalytic methaneconversion process.

BACKGROUND OF THE INVENTION

It is the business of many refineries and chemical plants to obtain,process and upgrade relatively low value hydrocarbons to more valuablefeeds, or chemical raw materials. For example, methane, the simplest ofthe saturated hydrocarbons, is often available in rather largequantities either as an undesirable by product in admixture with othermore valuable higher molecular weight hydrocarbons, or as a component ofan off gas from a process unit, or units. Though methane is useful insome chemical reactions, e.g., as a reactant in the commercialproduction of methanol and formaldehyde, it is not as useful a chemicalraw material as most of the higher molecular weight hydrocarbons. Forthis reason process streams which contain methane are usually burned asfuel.

Methane is also the principal component of natural gas, which iscomposed of an admixture of normally gaseous hydrocarbons ranging C₄ andlighter and consists principally of methane admixed with ethane,propane, butane and other saturated, and some unsaturated hydrocarbons.Natural gas is produced in considerable quantities in oil and gasfields, often at remote locations and in difficult terrains, e.g.,offshore sites, arctic sites, swamps, deserts and the like. Under suchcircumstances the natural gas is often flared while the oil isrecovered, or the gas is shut in, if the field is too remote for the gasto be recovered on a commercial basis. The construction of pipelines tocarry the gas is often not economical, due particularly to the costs ofconnecting numerous well sites with a main line. Transport of naturalgas under such circumstances is also uneconomical because methane atatmospheric pressure boils at -258° F. and transportation economicsdictate that the gas be liquefiable at substantially atmosphericpressures to reduce its volume. Even though natural gas containscomponents higher boiling than methane, and such mixtures. can beliquefied at somewhat higher temperatures than pure methane, thetemperatures required for condensation of the admixture is nonethelesstoo low for natural gas to be liquefied and shipped economically. Underthese circumstances the natural gas, or methane, is not even ofsufficient value for use as fuel, and it is wasted.

The thought of utilizing methane from these sources, particularlyavoiding the tremendous and absolute waste of a natural resource in thismanner, has challenged many minds, but has produced few solutions. It ishighly desirable to convert methane to hydrocarbons of higher molecularweight (hereinafter, C₂ +) than methane, particularly admixtures of C₂ +hydrocarbon products which can be economically liquefied at remotesites; especially admixtures of C₂ + hydrocarbons rich in ethylene orbenzene, or both. Ethylene and benzene are known to be particularlyvaluable chemical raw materials for use in the petroleum, petrochemical,pharmaceutical, plastics and heavy chemicals industries. Ethylene isthus useful for the production of ethyl and ethylene compounds includingethyl alcohol, ethyl ethers, ethylbenzene, styrene, polyethylbenzenesethylene oxide, ethylene dichloride, ethylene dibromide, acetic acid,oligomers and polymers and the like. Benzene is useful in the productionof ethylbenzene, styrene, and numerous other alkyl aromatics which aresuitable as chemical and pharmaceutical intermediates, or suitable inthemselves as end products, e.g., as solvents or high octane gasolinecomponents.

It has been long known that methane, and natural gas can bepyrolytically converted to C₂ + hydrocarbons. For example, methane ornatural gas passed through a porcelain tube at moderate red heat willproduce ethylene and its more condensed homologs such as propylene, aswell as small amounts of acetylene and ethane. Methane and natural gashave also been pyrolytically converted to benzene, the benzene usuallyappearing in measurable quantities at temperatures above about 1650° F.(899° C.), and perhaps in quantities as high as 6-10 wt. % at 2200° F.to 2375° F., (1204° to 1302° C.) or higher. Acetylene and benzene inadmixture with other hydrocarbons, have been produced from methane andnatural gas in arc processes, cracking processes, or partial combustionprocesses at temperatures ranging above about 2775° F. (1524° C.). Heatfor such reactions has been supplied from various sources includingelectrically heated tubes, electric resistance elements, and spark orarc electric discharges. These processes characteristically requireconsiderable heat energy which, most often, is obtained from combustionof the by-product gases. The extreme temperatures coupled with the lowyields of higher molecular weight hydrocarbons such as benzene an otheraromatics have made the operation of such pyrolytic processesuneconomical.

High temperature, noncatalytic, thermal pyrolysis processes involvingthe conversion of methane in the presence of ethane and otherhydrocarbons are well known in the art. Representative articles include:Roczniki Chemi, An. Soc. Chim. Polonorum, 51, 1183 (1977), "TheInfluence of Ethane on Thermal Decomposition of Methane Studied By TheRadio Chromatographic Pulse Technique"; J. Soc. Chem. Ind. (Trans. andComm.) 1939,58, 323-7; and J. Chin. Chem. Soc. (Taipei) 1983, 30(3),179-83.

Addition of hydrogen to pyrolysis reaction mixtures is well known, seefor example, pp 84-85 in "Pyrolysis Theory and Industrial Practice", L.F. Albright, B. L. Crynes and W. H. Corcoran (Ed.), Academic Press(1983).

Partial oxidation processes of converting methane to C₂ + hydrocarbonsare well known. In these processes, hydrogen must be removed either aswater, molecular hydrogen or other hydrogen-containing species.Likewise, any other polymerization mechanism wherein methane isconverted to C₂ + hydrocarbon products requires a tremendous amount ofenergy, most often supplied as heat, to provide the driving force forthe reactions. In the past the molecular hydrogen liberated by thereaction has often been separated and burned to provide the necessaryprocess heat. This route has proven an abomination to the production ofC₂ + hydrocarbons, but alternate reaction pathways have appeared littlebetter, if any, for these have resulted in the production of largequantities of the higher, less useful hydrogen deficient polymericmaterials such as coke, and highly oxidized products such as carbondioxide and water.

Typical of low temperature prior art oxidation processes are thosedisclosed in U.S. Pat. Nos. 4,239,658, 4,205,194 and 4,172,180 which usea regenerable catalyst-reagent U.S Pat. No. 4,239,658, for example,teaches a process for the conversion of methane to higher molecularweight hydrocarbons. In the process, a three component catalyst-reagentis utilized which comprises a mixture of various metals and metaloxides, particularly a Group VIII noble metal, nickel or a Group VI-Bnoble metal, a Group VI-B metal oxide and a Group II-A metal. The patentteaches process temperatures from about 1150° to 1600° F. (621° to 871°C.), preferably 1250° F. to about 1350° F. (677° to 732° C.).

It has also been reported in Science 153, 1393, (1966), "HighTemperature Synthesis of Aromatic Hydrocarbons From Methane", thataromatic hydrocarbons can be prepared from methane by contact withsilica at 1000° C. (1832° F.). The yield of hydrocarbons was in therange of 4.8 to 7.2 percent based on the methane used in a single passat a space velocity of 1224 hr⁻¹.

In the J. Chinese Chem. Soc., Volume 29, pages 263-273 (1981), it isreported that methane can be converted to C₂ + hydrocarbons attemperatures of 800° to 1130° C. and space velocities of 3100 hr⁻¹ orless using a metal oxide catalyst. However, the total conversion ofmethane, at best, is 7.5 mole percent using a thorium oxide catalyst.

Franz Fischer, reports in an article entitled: "The Synthesis of BenzolHydrocarbons From Methane At Ordinary Pressure and Without Catalyst"(Brennstoff-Chemie, Vol. 9, pp. 309-316, 1928) that methane is convertedto benzol hydrocarbons by passing methane through a hot tube. Incarrying out this work Fischer tested many substances for catalyticactivity at temperatures ranging from 650° to 1150° C. and at high flowrates and concluded that the substances tested were not catalytic andnot necessary. Among the substances tested were elemental iron, copper,tungsten, molybdenum, tin and carbon; and the compounds potassiumhydroxide and silica gel.

SUMMARY OF THE INVENTION

In a continuous catalytic process for the production of higher molecularweight hydrocarbons from lower molecular weight hydrocarbons in which alower molecular weight hydrocarbon containing gas is contacted in areaction zone with a higher molecular weight hydrocarbon synthesiscatalyst under C₂ + hydrocarbon synthesis conditions, the improvementcomprising adding hydrogen to said gas thereby forming a reaction gaswherein said hydrogen comprises 1 to 25 volume percent of the reactiongas, said synthesis conditions including a temperature greater than1000° C. and a gas hourly space velocity of greater than 3200 hr⁻¹.

DETAILED DESCRIPTION OF THE INVENTION

It has been found in the present invention that in the catalyticconversion of lower molecular weight hydrocarbons to higher molecularweight hydrocarbons that the yield of higher molecular weighthydrocarbons, particularly the light aromatics, are dramaticallyincreased by the addition of a small amount of hydrogen to the feed gas.

As used in the present invention the phrase "lower molecular weighthydrocarbons" means hydrocarbons containing at least one or more carbonatoms, i.e., methane, ethane, propane, etc. Also as used in the presentinvention, the phrase "higher molecular weight hydrocarbons" meanshydrocarbons containing two or more carbon atoms and at least one carbonatom more than the lower molecular weight hydrocarbon in the feedstock.

As used herein the phrase "C₂ + hydrocarbon synthesis conditions" refersto the selection of feedstock, reaction temperature, space velocity andcatalyst described hereafter such that higher molecular weighthydrocarbons are produced in the process with yields as describedhereafter. Other process parameters necessary to maintain C₂ +hydrocarbon synthesis conditions, such as the selection of particulartypes of reaction vessels, etc., is readily determined by any personskilled in the art.

As used in the present invention the word "metal" refers to all thoseelements of the periodic table which are not non-metals. "Non-metals"for the purpose of the present invention refers to those elements havingatomic numbers 1, 2, 5 through 10, 14 through 18, 33 through 36, 52through 54, 85 and 86.

The word "catalyst" is used in the present invention to mean a substancewhich strongly affects the rate of a chemical reaction but which itselfundergoes no chemical change although it may be altered physically bychemically absorbed molecules of the reactants and reaction products.

As used in the present invention the phrase "continuous catalyticprocess" means a process in which feedstock and products aresimultaneously fed to and removed from a reaction zone containing acatalyst.

As used in the present invention the phrase "reaction gas" refers to thegas or gas mixture being fed to the catalyst-containing reaction zone.

As used in the present invention the words "light aromatics" refers tosingle ring aromatic hydrocarbons, for example, benzene, toluene,xylenes, and so forth.

The Reaction Gas and Products

The reaction gas of the present invention will comprise lower molecularweight hydrocarbons and sufficient added hydrogen to significantlyincrease the yield of light aromatic hydrocarbons. The lower molecularweight hydrocarbon will comprise methane or natural gas containing C₁ toC₄ hydrocarbons.

Generally enough hydrogen is added to increase the the yield of lightaromatic hydrocarbons by 10 to 40 weight percent as compared to areaction gas consisting of 100% methane. Generally, the hydrogen isadded so that the reaction gas comprises 1 to 25 volume percent addedhydrogen. Preferably, the added hydrogen content in the reaction gascomprises 2 to 20 volume percent and more preferably 5 to 15 volumepercent.

The reaction gas can also contain other nonhydrocarbon gases such asnitrogen and carbon dioxide.

The product higher molecular weight hydrocarbons will comprise C₂ +hydrocarbons, particularly mixtures of C₂ + hydrocarbons which can beeconomically liquefied. Preferably, the higher molecular weighthydrocarbon product streams will be rich in ethylene or aromatics suchas benzene, or both. The product stream will also contain copiousamounts of hydrogen. The hydrogen added to the reaction gas can ofcourse be obtained from the product gas.

The process of the present invention affords high conversions of thelower molecular weight hydrocarbons with high selectivity to highermolecular weight hydrocarbons. More particularly, as measured by thedisappearance of the lower molecular weight hydrocarbons, the process ofthe present invention affords conversions of 19 mole percent or more ofthe lower molecular weight hydrocarbons, and preferably, the conversionsare greater than 25 mole percent and more preferably greater than 40mole percent. The carbon-containing reaction products comprise 80 molepercent or more of higher molecular weight hydrocarbons, preferably,greater than 90 mole percent. Based on the feed, at least 15 molepercent, and preferably at least 20 mole percent, and more preferably atleast 40 mole percent of the lower molecular weight hydrocarbons isconverted to higher molecular weight hydrocarbons which is referred toherein as selectivity.

Process Conditions

It is essential to the process of the present invention that a hightemperature greater than 1000° C. is maintained in the reaction zonealong with a high gas hourly space velocity of greater than 3200 hr⁻¹.Preferably, the temperature will be greater than 1100° C. with a spacevelocity greater than 6000 hr⁻¹. Still more preferably the temperatureis greater than 1150° C. with a space velocity greater than 9000 hr⁻¹.

Generally, the temperature will be in the range of 1001° to 1300° C.while the gas hourly space velocity is in the range 3200 to 360,000hr⁻¹. Preferably, the temperature is in the range 1100° to 1200° C. witha gas hourly space velocity of 6,000 to 36,000 hr⁻¹. More preferably thetemperature is in the range 1150° to 1175° C. with a gas hourly spacevelocity in the range of 9,000 to 18,000 hr⁻¹. Generally, hightemperatures are used with high space velocities and low temperaturesare used with low space velocities.

The process can be operated at sub-atmospheric, atmospheric, or supraatmospheric pressure to react and form the higher molecular weight C₂ +hydrocarbons. It is preferred to operate at atmospheric pressure orwithin about 15 psi of atmospheric pressure.

The Catalysts

The lower molecular weight hydrocarbons is introduced into a reactionzone containing a suitable hydrocarbon synthesis catalyst. Thereaction-zone catalyst system can be either of the fixed bed type orfluid bed type and the lower molecular weight hydrocarbons can beintroduced into the top or bottom of the reaction zone with the productstream removed from either the top or bottom. Preferably, a fixed bedcatalyst system is used and the feed stream is introduced into the topof the reaction zone and product is withdrawn from the bottom.

A wide range of catalysts can be used in the present invention. Manycommercially available catalysts which have been used in differentprocesses are suitable for use in the process of the present invention.The word "catalyst" is used in the present invention to mean a substancewhich strongly affects the rate of a chemical reaction but which itselfundergoes no chemical change although it may be altered physically bychemically absorbed molecules of the reactants and reaction products. Itis also understood that the catalyst of the present invention may beformed in situ. For example, in the present invention when an oxide,nitride, or carbide metal catalyst is initially charged to the reactor,the oxide and nitride may be converted in situ to the carbide which thenfunctions as the catalytic species.

Catalysts useful in the present invention may be used with and withoutcatalyst supports. However, it is generally preferred to use a catalystsupport such as the well known aluminas.

The catalysts useful in the present invention may have a wide range ofsurface areas as measured by the BET method using krypton [Jour. Am.Chem. Soc., vol. 60, pp 309 (1938)]. Low surface areas are preferred.Generally, the catalyst will have a surface area in the range 0.1 to 10m² /gram, preferably in the range 0.2 to 2.0 m² /gram.

The hydrocarbon synthesis catalysts useful in the present invention willprovide conversion of at least 19% of the lower molecular weighthydrocarbons and will maintain this conversion for at least 3 hoursunder the temperature and space velocity conditions previouslydiscussed. Preferred catalysts of the present invention will provideconversions of 30% or more of the lower molecular weight hydrocarbonsfeed and remain active for 3 hours or more.

Particularly preferred catalysts are those described in our copendingapplication entitled "Conversion of Low Molecular Weight Hydrocarbons toHigher Molecular Weight Hydrocarbons Using a Metal-containing Catalyst",Ser. No. 547,699, filed Oct. 31, 1983, the entire disclosure of which isincorporated herein by reference. A useful silicon-containing catalystis disclosed in our copending application entitled: "Conversions of LowMolecular Weight Hydrocarbons to Higher Molecular Weight HydrocarbonsUsing a Silicon Compound-Containing Catalyst", Ser. No. 547,697, filedOct. 31, 1983, the disclosure of which is incorporated herein byreference. A useful boron compound containing catalyt is described inU.S. Pat. No. 4,507,517, the disclosure of which is incorporated hereinby reference.

The hydrocarbon synthesis catalysts useful in the present invention maybe a metal compound-containing catalyst or non-metal compound-containingcatalyst or mixtures thereof.

Metal-Compound Containing Catalysts

A wide range of metal compound-containing catalysts and catalystsupports may be used in the present invention.

Representative metal compound-containing catalysts are refractorymaterials and include the compounds of the Group I-A, II-A, III-A, IV-Bor actinide series metals. Representative compounds include the carbide,nitride, boride or oxide of a Group I-A, II-A, III-A, IV-B or actinideseries metal, used alone or in combination.

The catalyst must be thermally stable under the operating condition inthe reaction zones and are preferably particulate in form. The carbidesof the Groups I-A, II-A, III-A, IV-B and actinide series metals areparticularly preferred because it is believed that the carbide metalcompound-containing catalyst are the most stable under the severereaction conditions of the present invention. Preferably, the catalystcan also be regenerated by the periodic burning-off of any undesirabledeposits such as coke. The regeneration of catalyst by the burning offcoke is well known in the catalyst and petroleum processing art.

Representative Group I-A metal compound-containing catalyst include thecarbide, nitride, boride, oxide of lithium, sodium, potassium, rubidium,and cesium. Most preferred among the Group I-A metals is lithium.

Representative Group II-A metal compound-containing catalysts includethe carbide, nitride, boride, or oxide of beryllium, magnesium, calcium,strontium, barium, and radium. Most preferred among the Group II-Ametals is calcium.

Representative Group III-A metal compound-containing catalysts includethe carbide, nitride, boride, or oxide of aluminum, scandium, yttrium,lanthanum, and actinium. Most preferred among the Group III-A metals isaluminum.

Representative Group IV-B metal compound-containing catalysts includethe carbide, nitride, boride, or oxide of titanium, zirconium, hafnium,and zirconium. Most preferred among the Group IV-B metals is zirconium.Representative actinide series metal compound-containing catalystsinclude the carbide, nitride, boride, or oxide of thorium and uranium.Most preferred among the actinide series metals is thorium.

A particularly preferred catalyst for use in the present invention isthorium oxide on alumina.

Non-Metal Compound Containing Catalysts

Representative non-metal compound containing catalysts are catalystscontaining compounds of boron and silicon.

Representative boron compound containing catalysts are refractorymaterials and include boron carbide, or boron nitride. Particularlypreferred is boron nitride.

Representative silicon compound-containing catalysts are refractorymaterials and include silicon carbide, nitride, silicon boride orsilicon oxide. Particularly preferred is silicon carbide.

The advantages of the present invention will be readily apparent from aconsideration of the following examples.

The examples illustrating the invention were carried out as follows:

The apparatus comprises a vertical reactor tube made of high purityalumina of 3/8" O.D. and 1/4" I.D. This tube is 24" long, the central12" of which is surrounded by a high temperature electric furnace(Marshall Model 1134). The heated section of the tube is packed with thetest catalyst. A small piece of close fitting alumina honeycomb, ormonolith, at the bottom of the bed supports the catalyst. An "O"-ringsealed closure at the top of the reactor tube connects it to a gas flowsystem, which permits either argon or methane to be passed into thereactor at a measured rate. Gas flows into the reactor are measured withpre-calibrated flowmeters. Gas exiting from the reactor is first passedthrough a trap packed with dry stainless steel "saddles" (distillationcolumn packing), then through a tube fitted with a rubber septum. Gassamples are taken through the septum with a syringe. Off gas exits thesystem through a "U"-tube partially filled with oil. Bubbles passingthrough the oil provide a visual indicator of the gas flow.

In operation, the central section of the reactor tube is packed with thecatalyst to be tested. The catalyst particles range in size from 8 meshto 12 mesh. About 10 cm³ of catalyst is charged to the reactor. Thereactor is then placed in the cold furnace, and the necessary input andoutput connections are made. A slow flow of about 15 to 20 ml/min. ofargon is continuously passed through the reactor, which is then broughtto the desired temperature over a period of about 150 min. Temperatures.reported herein are measured in the furnace wall. Temperatures aremeasured by a thermocouple mounted in the furnace wall. Calibrationcurves, previously developed from a thermocouple in the catalyst bed andcompared to the furnace wall thermocouple, are used to determine thereaction temperatures reported herein.

Once the apparatus is at the desired temperature, argon flow is stoppedand methane flow is started at the predetermined flow rate. Spacevelocities are calculated on the basis of the temperature, pressure,methane flow rate into the reactor and on the catalyst bed dimensions.On each run, the reaction is allowed to level out for 15 to 20 minutesbefore the first analytic sample is withdrawn through the septum. Twosamples are taken each time, using one ml gas-tight syringes. Aliquotsof these samples (0.25 ml) are separately injected into a gaschromatograph packed with Poropak Q. Analysis is made for hydrogen,methane, and light hydrocarbons having less than 5 atoms of carbon.Other aliquots of the same samples are injected into another gaschromatograph column packed with Bentone 1200. This analysis is made foraromatics, including benzene, toluene, xylenes, etc.

EXAMPLES

The Tables below illustrate the effect of adding hydrogen to thereaction feed gas in the conversion of methane.

                  TABLE I                                                         ______________________________________                                        Constant Conversion of 18%, GHSV = 9000 hr.sup.-1                                                     % Converted Carbon                                                            Atoms Appearing as                                    Temperature,                                                                              % H.sub.2   Light Aromatics in                                    °C.  (Balance CH.sub.4)                                                                        the Product                                           ______________________________________                                        1125         0          47                                                    1150        15          55                                                    1150        20          53                                                    1150        25          60                                                    ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Constant Conversion of 25%, GHSV = 9000 hr.sup.-1                                                     % Converted Carbon                                                            Atoms Appearing as                                    Temperature,                                                                              % H.sub.2   Light Aromatics in                                    °C.  (Balance CH.sub.4)                                                                        the Product                                           ______________________________________                                        1145         0          40                                                    1160        15          51                                                    1160        20          52                                                    1160        25          53                                                    ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Constant Conversion of 30%, GHSV = 9000 hr.sup.-1                                                     % Converted Carbon                                                            Atoms Appearing as                                    Temperature,                                                                              % H.sub.2   Light Aromatics in                                    °C.  (Balance CH.sub.4)                                                                        the Product                                           ______________________________________                                        1150         0          36                                                    1175        15          36                                                    1170        20          43                                                    1175        25          46                                                    ______________________________________                                    

Addition of H₂ to the methane feed gas requires that the temperature ofthe reaction zone be raised to maintain conversion at a constant spacevelocity. The beneficial effect of adding hydrogen is evidenced by theincrease in the fraction of converted carbon appearing as the mostdesirable product, the light aromatics. Thus, hydrogen addition improvesthe selectivity of the catalytic conversion of methane.

The catalyst used in obtaining the data in the tables was prepared asfollows. A low area support was prepared by crushing Carborundum Companyfused white refractory alumina bubbles, sieving the crushed material,and retaining the 8-20 mesh fraction. The 20 g of this support wasadded, dropwise, a solution of 2.46 g Th(NO₃)₄.4H₂ O dissolved in 4 mldistilled water. After mixing throughly with a spatula, the mixture wasdried at 155° C. overnight in an oven, then fired at 900° C. in air toconvert Th(NO₃)₄ to ThO₂. For these experiments, the inside of thealumina reactor tube was coated with copper, by exposing it to asolution of 7 g of Cu(C₂ H₃ O₂)₂.H₂ O in methanol three times, drainingand drying the tube between each exposure, then reducing the adsorbedcopper salt to metallic copper for reduction in hydrogen at 300° C. Toassure there was no excess of copper, the reactor tube temperature wasincreased to 1150° C., and an argon flow maintained through the tube for10 hours at the elevated temperature.

The above data illustrates one preferred embodiment of the invention andthe increased yield of light aromatic hydrocarbons by the addition of asmall but effective amount of hydrogen added to the feed gas.

What is claimed is:
 1. In a continuous catalytic process for theproduction of higher molecular weight hydrocarbons from lower molecularweight hydrocarbons in which a lower molecular weight hydrocarboncontaining gas is contacted in a reaction zone with a higher molecuilarweight hydrocarbon synthesis catalyst under C₂ + hydrocarbon synthesisconditions, the improvement comprising significantly increasing theproduction of light aromatics by 10 to 40 weight percent by addinghydrogen to said gas thereby forming a reaction gas wherein saidhydrogen comprises 1 to b 25 volume percent of the reaction gas, saidsynthesis conditions including a temperature greater than 1000° C. and agas hourly space velocity of greater than 3200 hr⁻¹.
 2. The process ofclaim 1 wherein said reaction zone contains a stationary or fluidizedbed of a catalyst containing a carbide, nitride, boride or oxide of aGroup I-A, II-A, III-A, IV-B or actinide series metal.
 3. The process ofclaim 2 wherein said temperature is in the range of 1100° to 1200° C.,said space velocity is in the range of 6000 to 36,000 hr⁻¹ and at least20 mole percent of said lower molecular weight hydrocarbons is convertedto higher molecular weight hydrocarbons.
 4. The process of claim 3wherein said added hydrogen comprises 2 to 20 volume percent of thereaction gas.
 5. The process of claim 4 wherein said catalyst contains aGroup I-A metal selected from lithium, potassium or cesium.
 6. Theprocess of claim 4 wherein said catalyst contains a Group II-A metalselected from beryllium, magnesium, calcium, strontium, barium orradium.
 7. The process of claim 4 wherein said catalyst contains a GroupIII-A metal selected from aluminum, scandium, yttrium, lanthanum andactinium.
 8. The process of claim 4 wherein said catalyst contains aGroup IV-B metal selected from titanium, zircoium, and hafnium.
 9. Theprocess of claim 1 wherein said catalyst contains thorium or uranium.10. The process of claim 1 wherein said catalyst contains a boroncompound.
 11. The process of claim 1 wherein said catalyst contains asilicon compound.
 12. The process of claim 4 wherein said highermolecular weight hydrocarbon stream is rich in ethylene or aromatics orboth.
 13. In a continuous catalytic process for the production of highermolecular weight hydrocarbons from lower molecular weight hydrocarbonsin which a lower molecular weight hydrocarbon containing gas iscontacted in a reaction zone with a higher molecular weight hydrocarbonsynthesis catalyst under C₂ + hydrocarbon synthesis conditions, theimprovement comprising significantly increasing the production of lightaromatics by 10 to 40 weight percent by adding hydrogen to said gasthereby forming a reaction gas wherein said hydrogen comprises 2 to 20volume percent of the reaction gas, said synthesis conditions includinga temperature in the range of 1150° to 1175° C., a space velocity is inthe range of 9000 to 18,000 hr⁻¹ and wherein at least 40 mole percent ofsaid lower molecular weight hydrocarbons is converted to highermolecular weight hydrocarbons.
 14. The process of claim 13 wherein saidcatalyst contains a Group I-A metal selected from lithium, potassium orcesium.
 15. The process of claim 13 wherein said catalyst contains aGroup II-A metal selected from beryllium, magnesium, calcium, strontium,barium or radium.
 16. The process of claim 13 wherein said catalystcontains a Group III-A metal selected from aluminum, scandium, yttrium,lanthanum and actinium.
 17. The process of claim 13 wherein saidcatalyst contains a Group IV-B metal selected from titanium, zirconium,and hafnium.
 18. The process of claim 13 wherein said catalyst containsthorium or uranium.
 19. The process of claim 13 wherein said catalystcontains a boron compound.
 20. The process of claim 13 wherein saidcatalyst contains a silicon compound.
 21. The process of claim 13wherein said higher molecular weight hydrocarbon stream is rich inethylene or aromatics or both.
 22. In a continuous catalytic process forthe production of higher molecular weight hydrocarbons from lowermolecular weight hydrocarbons in which a lower molecular weighthydrocarbon containing gas is contacted in a reaction zone with a highermolecular weight hydrocarbon synthesis catalyst under C₂ + hydrocarbonsynthesis conditions, the improvement comprising significantlyincreasing the production of light aromatics by 10 to 40 weight percentby adding hydrogen to said gas thereby forming a reaction gas whereinsaid hydrogen comprises 5 to 15 volume percent of the reaction gas, saidsynthesis conditions including a temperature in the range of 1150° to1175° C., a space velocity is in the range of 9000 to 18,000 hr⁻¹, saidcatalyst contains a carbide, nitride, boride or oxide of a Group I-A,II-A, III-A, IV-B or actinide series metal and wherein at least 40 molepercent of said lower molecular weight hydrocarbons is converted tohigher molecular weight hydrocarbons.
 23. The process of claim 1 whereinsaid lower molecular weight hydrocarbon consists of methane.
 24. Theprocess of claim 13, wherein said lower molecular weight hydrocarbonconsists of methane.
 25. The process of claim 22 wherein said lowermolecular weight hydrocarbon consists of methane.